2001 Pontiac Grand Prix Difficult starting.

Car was always being taken care of - preventive maintenance and etc.
I was on a hilly highway when I could not climb anymore, I almost felt like driving in nuetral. I drove it in to a local machanic they ran it thru a computerized check and it came back with the following codes: P0131, P0300 & P0404. They diagnozed it and reported that they found a hole in the upper plenum. They replaced the "Upper Intake Manifold", did a complete tune-up (spark plugs & wires, fuel filter & air filter), they also claimed that the fuel pump is bad which is plugging the Catalytic Converter, they replaced both (the Catalytic converter used is not a Delphi part).
It ran fine but I had difficult starting it in the morning or when not used for long period of time (sometimes so bad, that I lost power as soon as I stopped pushing the gas pedal - in park, drive and nuetral), I took it back to them - they claimed that the Fuel Pump is defective and they changed it for me.
Now. The starting issue is better than it was, but I still have a problem starting it in the morning and when not used a period of time - I have to raise the engine (pushing the gas pedal) at the time of starting or it will just not start.
When I left the mechanic the last time they told me that if this will not do it, it might be the fuel injectors. I just put in about $2,200, and I hate to throw good money after bad money. Is there anything else you can suggest?